Texas/New Mexico/Louisiana/Mexico Obs And Discussion Thread Part 4

[Srain]

The 12Z NAM (WRF/NMM) as well as the GFS are a tad more bullish that a line of showers/storms develop just ahead of the short wave crossing the area tomorrow and attending cold frontal passage. We will see.

[Srain]

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1116 AM CST SUN NOV 25 2012

VALID 261200Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN TX INTO LA...SRN

AR...AND FAR WRN MS...

...SYNOPSIS...

A COLD FRONT WILL EXTEND FROM CNTRL TX INTO CNTRL AR AND TO THE OH

RIVER BY LATE AFTERNOON...AND WILL SURGE SWD TO A TX COAST TO SRN

APPALACHIAN LINE BY TUE MORNING. THIS FRONT WILL BE DRIVEN SWD BY

STRONG NWLY FLOW ACROSS THE CNTRL U.S. WHERE AN UPPER TROUGH AXIS

WILL BE AT 00Z. A SRN STREAM SHORTWAVE WILL ALSO BE MOVING ACROSS

NRN MEXICO...ARRIVING IN CNTRL/ERN TX DURING THE EVENING.

AHEAD OF THE COLD FRONT...HEATING WILL LEAD TO WEAK LOW PRESSURE

OVER CNTRL AND ERN TX...WHERE SSWLY SURFACE WINDS WILL HELP MAINTAIN

DEWPOINTS IN THE 60S F. THIS...ALONG WITH COOL AIR ALOFT AND FORCING

ALONG THE FRONT SHOULD RESULT IN SCATTERED THUNDERSTORMS...SOME

SEVERE FROM E CNTRL TX TO THE MS RIVER.

...E TX INTO LA...SRN AR...WRN MS...

AREAS OF RAIN AND ELEVATED THUNDERSTORMS ARE EXPECTED TO INCREASE BY

MID MORNING FROM SRN AR INTO MS...BUT THESE SHOULD NOT BE SEVERE.

DAYTIME HEATING AND COOLING PROFILES ALOFT WILL LEAD TO MUCAPE ON

THE ORDER OF 1500-2000 J/KG FROM E CNTRL TX INTO NRN LA. WITH FULL

HEATING AND SWLY WINDS OVER CNTRL TX...THIS IS WHERE THE LOW LEVEL

LAPSE RATE PLUME WILL BE POINTED. THUS...INITIAL DEVELOPMENT IS

EXPECTED THERE...POSSIBLY HIGH BASED. FURTHER DEVELOPMENT WILL THEN

OCCUR NEWD ALONG THE ADVANCING COLD FRONT.

DEEP LAYER SHEAR WILL BE MOST FAVORABLE FOR SUPERCELLS ACROSS ERN TX

AND INTO SRN AR AND LA...WHERE MIDLEVEL WINDS WILL BE DUE WLY.

HERE...SUPERCELLS CAPABLE OF LARGE HAIL WILL BE LIKELY. COMBINED

PARAMETERS IN PLACE WILL GENERALLY FAVOR MAXIMUM HAIL SIZES AROUND

GOLF BALL...PERHAPS AS HIGH AS 2.00". HOWEVER...A SUBTLE VEER-BACK

WIND PROFILE IN THE 700-500 MB LAYER MAY HAVE AN ADVERSE IMPACT ON

STORM STRUCTURE. REGARDLESS...SEVERE HAIL GREATER THAN 1.00" IS

LIKELY.

DAMAGING WINDS MAY ALSO OCCUR...ESPECIALLY WITH THE ACTIVITY THAT

FORMS OVER CNTRL TX IN THE HEAT. THESE STORMS WILL LIKELY PERSIST

AND PROPAGATE ESEWD...POSSIBLY AFFECTING THE HOUSTON AREA AFTER

MIDNIGHT.

OVERALL...LOW LEVEL SHEAR WILL BE MARGINAL FOR TORNADOES...WITH ONLY

A LOW THREAT WITH THE INITIAL DEVELOPMENT BEFORE IT MERGES INTO A

LINE.

..JEWELL.. 11/25/2012

[Srain]

Morning e-mail from Jeff:

Good chance for thunderstorms tonight ahead of the next cold front.

First item this morning is the dense fog over parts of the area, mainly WSW and SW of metro Houston and into the coastal bend and central TX. Should see this fog blanket erode by mid morning, but between now and then visibilities will be on the low side running in the .25 of a mile to 1 mile range in the advisory area.

Also seeing a few showers on the radar…a rare sight…mainly along the coast and then inland over far SE Galveston County and Chambers County. These showers are along the leading edge of a deeper push of moisture off the western Gulf where dewpoints are running in the upper 60’s. Fairly impressive moisture return has taken place in the last 24 hours with morning lows today running some 30 degrees warmer over Sunday morning. Fast moving upper level storm is noted over Baja this morning tracking eastward while the next cold front is advancing down the plains into north TX. Combination of the approaching disturbance from the SW and front from the north along with decent moisture profile should support the best chance of rainfall this area has seen in a while tonight.

Moisture will continue to increase off the Gulf today as lower pressure over NW TX favor onshore winds. Will likely continue to see a few scattered showers move inland off the Gulf in the warm air advection pattern, but the main event will come after dark as large scale forcing moves into the area from the SW near/ahead of the approaching cold front. Front should reach our northern counties in the 10pm-midnight time period and push off the coast by 300-600am Tuesday. Shorter term meso models are not overly impressive with rain chances along the boundary with most of the “action” focused east of the area in Louisiana where SPC slight risk area currently is in place. While parameters looks overall favorable for some severe weather this evening/overnight, think the risk is on the lower end of the spectrum. While models fully erode a weak cap over the region by late this afternoon, they may be a little fast in reducing this feature and the larger values of CAPE (instability) suggested also seems overdone given winds turning more SSW prior to the front and boundary layer cooling during the evening hours. Still expect to see widespread thunderstorms develop with favorable moisture influx and good lift from multiple sources, but think the severe threat will be limited to areas east of I-45 and even in this area the threat appears isolated. With that said, there could be some enhancement of low level shear in the corridor from roughly Coldspring to Liberty to Galveston overnight which could slightly favor a very small increase in the threat for tornado production is this area. Interestingly enough the regional WRF models suggest the bulk of the activity will affect areas west and southwest of Houston this evening/overnight or the counties of Jackson, Wharton, Matagorda, Brazoria, and Fort Bend…this could be a function of this area seeing the greatest amounts of sun today and instability last longer into the evening hours when the best forcing will arrive.

Overall most of the area should see at least some rainfall, although I would like to see more coverage and organization of convection on the meso models to be more confident that the W and NW areas will in fact see some activity. Best coverage will be over the central and eastern counties and then east into Louisiana. A general .50 of an inch to possibly an inch is expected which will help ease some of the developing dryness. Areas that do not see much rainfall tonight could see an elevated fire risk on Tuesday as a dry air mass and gusty NW winds move into the region behind the overnight storm system. Main concern would be north of I-10 where fine fuels are cured and dry and over Brazoria County where KBDI values are highest.

Fast progressive pattern will keep the bulk of the cold air bottled in Canada with only quick shots every 2-3 days as storm systems race across the US. Next system will cross TX Thursday/Friday. While such patterns usually favor overall dry conditions over the state, the next system does also show some potential for rains especially along the coast where coastal troughing over the western Gulf may spread moisture northward into the coastal bend and SE TX starting Thursday. Given the dry pattern of late, would like to see more model support for this event before suggesting better rain chances in the Thurs/Fri period, but it does look promising this morning. After the front tonight, there appears to be little cold air to drop southward as the persistent vortex over the Gulf of Alaska keeps the flow west to east over the US and cold air trapped from flowing southward. Even into the first week of December the temperatures look balmy with lows in the 50’s/60’s and highs in the 70’s/near 80.

[Ed Lizard]

GFS under a quarter of an inch, NAM near a quarter, that would be disappointing.

And if we do get cold, miserable weather this Winter, I suspect those brave tropical and subtropical plants growing in our temperate climate,, where there is nothing between Siberia and my yard but barb wire fences, would be particularly stressed by the drought and vulnerable to the sometimes bitter weather life in the mid-Latitudes brings.

[Srain]

MESOSCALE DISCUSSION 2123

NWS STORM PREDICTION CENTER NORMAN OK

0334 PM CST MON NOV 26 2012

AREAS AFFECTED...NERN TX...NRN LA...EXTREME SRN AR

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 262134Z - 262300Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...THUNDERSTORMS ARE FORECAST TO DEVELOP ACROSS NERN TX...NRN

LA AND EXTREME SRN AR LATE THIS AFTERNOON AND EVENING. ACTIVITY WILL

EVENTUALLY EVOLVE INTO A LINE AS A COLD FRONT ADVANCES EWD ACROSS

THE AREA. STORMS WILL PRIMARILY POSE A DAMAGING WIND AND LARGE HAIL

THREAT. A WW MAY NEED TO BE ISSUED DURING THE NEXT COUPLE OF HOURS.

DISCUSSION...MESOANALYSIS AT 21Z PLACES A SURFACE LOW IN FAR NERN

TX...WITH A WARM FRONT SLOWLY RETREATING EWD INTO CNTRL PORTIONS OF

LA...AND A COLD FRONT ADVANCING E-SEWD ACROSS CNTRL TX. AMPLE

SUNSHINE HAS AIDED IN WARM SECTOR TEMPERATURES WARMING INTO THE 70S

TO LOW 80S...WHILE AN AXIS OF LOW TO MID 60S DEWPOINTS EXTENDS

N-NEWD FROM THE TX GULF COAST INTO WRN LA. THE WARM/MOIST BOUNDARY

LAYER COMBINED WITH 700-500 MB LAPSE RATES NEAR 7 C/KM IS YIELDING

MLCAPE VALUES ESTIMATED TO BE AROUND 1000-2000 J/KG AHEAD OF THE

COLD FRONT.

VISIBLE SATELLITE IMAGERY AS OF 2115Z SHOWS THE WARM SECTOR IS

CAPPED...WHICH IS ALSO SUPPORTED BY 18Z SHV RAOB.

HOWEVER...LARGE-SCALE ASCENT ASSOCIATED WITH A SERIES OF SRN STREAM

DISTURBANCES EMANATING OUT OF NRN MEXICO...COMBINED WITH FRONTAL

CONVERGENCE/ASCENT ARE FORECAST TO ERODE THE CAPPING INVERSION

DURING THE 22-00Z TIME PERIOD. THIS WILL FAVOR THUNDERSTORM

DEVELOPMENT ALONG THE COLD FRONT AND PERHAPS EWD INVOF THE SURFACE

LOW AND WARM FRONT. DEEP-LAYER SHEAR ON THE ORDER OF 30-40 KT WILL

SUPPORT MULTICELL CLUSTERS AND PERHAPS A FEW SUPERCELLS POSING A

THREAT FOR LARGE HAIL AND DAMAGING WIND GUSTS. LOW-LEVEL SHEAR

PROFILES WILL NOT BE PARTICULARLY STRONG...THUS ANY TORNADO THREAT

IS EXPECTED TO BE BRIEF AND FOCUSED NEAR THE LOW WHERE BACKED

SURFACE WINDS WILL BE MOST PROBABLE.

BY NIGHT...STORMS ARE FORECAST TO ORGANIZE INTO A LINE AS THE COLD

FRONT ADVANCES EWD...WITH THE THREAT FOR HAIL AND STRONG/SVR WIND

GUSTS CONTINUING.

..GARNER/EDWARDS.. 11/26/2012

ATTN...WFO...JAN...LCH...SHV...HGX...FWD...

[Srain]

MESOSCALE DISCUSSION 2124

NWS STORM PREDICTION CENTER NORMAN OK

0508 PM CST MON NOV 26 2012

AREAS AFFECTED...PORTIONS OF CNTRL/SERN TX

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 262308Z - 270115Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...ISOLATED SVR STORMS WITH SVR HAIL AND POSSIBLY SVR WINDS

MAY BE OF CONCERN LATE THIS AFTERNOON INTO THE EVENING...AND THE

ISSUANCE OF A WW IS POSSIBLE.

DISCUSSION...A COLD FRONT EXTENDS FROM THE ARKLATEX SWWD ACROSS THE

EDWARDS PLATEAU AND FARTHER W INTO THE TRANS-PECOS REGION. A FRONTAL

INFLECTION NOTED E OF JUNCTION TX APPEARS TO BE THE FOCUS FOR A

SMALL...BUT PERSISTENT...AREA OF CONVECTION. RECENT STORM

DEVELOPMENT IS NOTED IN CNTRL TX ALONG A PREFRONTAL TROUGH THAT

DELINEATES THE WRN EDGE OF RICHER GULF MOISTURE AND EXTENDS FROM

JUST NORTH OF SHREVEPORT LA TO NORTH OF AUSTIN. DURING THE NEXT FEW

HOURS...STORM COVERAGE WILL LIKELY INCREASE ALONG THE PREFRONTAL

TROUGH...WEST OF WHICH A DEEPER BOUNDARY LAYER/STEEP LOW-LEVEL LAPSE

RATE ENVIRONMENT IS PRESENT. FURTHERMORE...MID-LEVEL ASCENT

OVERSPREADING THE AREA...IN ASSOCIATION WITH A VORT MAX ABOUT TO

EMERGE OVER CNTRL/SRN TX PER WATER VAPOR IMAGERY...MAY ALSO LEAD TO

AN UPTICK IN CONVECTION. MLCAPE VALUES OF 1500-2000 J/KG NEAR/SE OF

THE PREFRONTAL TROUGH WILL SUPPORT INTENSE UPDRAFTS WITH SVR HAIL

POSSIBLE...THOUGH ONLY MODEST MID-LEVEL FLOW/DEEP SHEAR COULD LIMIT

THE THREAT. SVR WINDS MAY ALSO BE POSSIBLE...THOUGH THE UNDERCUTTING

NATURE OF THE COLD FRONT MAY MITIGATE THIS CONCERN.

..COHEN/DARROW.. 11/26/2012

ATTN...WFO...LCH...HGX...FWD...EWX...

[Ed Lizard]

BULLETIN - EAS ACTIVATION REQUESTED

SEVERE THUNDERSTORM WARNING

NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX

521 PM CST MON NOV 26 2012

THE NATIONAL WEATHER SERVICE IN AUSTIN SAN ANTONIO HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...

SOUTHERN BURNET COUNTY...

NORTHWESTERN TRAVIS COUNTY...

EXTREME WEST CENTRAL WILLIAMSON COUNTY...

* UNTIL 600 PM CST.

* AT 512 PM CST...NWS METEOROLOGISTS HAVE DETECTED A SEVERE

THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZE HAIL...AND DAMAGING

WINDS IN EXCESS OF 60 MPH. THIS STORM WAS LOCATED NEAR MARBLE

FALLS...AND MOVING EAST AT 20 MPH.

* SOME LOCATIONS IN THE WARNING INCLUDE SPICEWOOD...SMITHWICK AND

LAGO VISTA.

[DoctorMu]

Action is visible WNW of CLL. Trough development should be interesting. Cluster might just be hooking right a bit.

[DoctorMu]

Yep, we're hooking. Rotation probable.

Edit: Nice trough net up

[DoctorMu]

little bow in that echo?

[DoctorMu]

My apologies for the grainy novice amateur attempt at capturing a small wallcloud backlit by lightning using a dumbphone. This is NW towards Bryan.

[msp]

got hit pretty hard on campus. we were inside at the time, but a friend mentioned that we got small hail and plenty of high winds.

[Ed Lizard]

2:30 am some thunder, lightning, judging by local stations, HGX NexRad, one to two tenths of rain, or, essentially squat.

[DoctorMu]

got hit pretty hard on campus. we were inside at the time, but a friend mentioned that we got small hail and plenty of high winds.

Not surprised. That cloud traveling NE would have traversed right over campus before heading to Bryan and in the direction of Madisonville.

[Srain]

Morning e-mail from Jeff:

Little hope for meaningful rainfall for at least the next 7 days and possibly well into mid December. Additionally, cold air will stay bottled up in Canada with this fast paced zonal flow in place across the US blocking any cold air intrusions.

Zonal flow aloft (west to east) is pushing the cool high pressure from the Monday night frontal passage eastward this morning with weak onshore winds starting to return to the area. This will be the last cold morning for several days as a strong storm system moving into the NW US coast and then into Canada will keep an onshore flow in place from today through at least Tuesday…possibly longer. Will see morning lows warm from the 40’s today to the 50’s on Friday and then the 60’s after Friday into next week. Afternoon highs will be downright balmy for early December in the upper 70’s and low 80’s under increasingly humid conditions. Temperatures will be running a solid 10 degrees above climate averages.

In the rainfall department…it would appear that drought has taken a foothold on the region as the weather system on Monday night was unable to produce good rainfall and the area will sink deeper into already moderate to severe drought. While a couple of weak disturbances will pass over the region in the WSW flow tonight and Friday, the quality and depth of moisture return off the western Gulf is poor and expect that only a few isolated showers may develop in the Matagorda Bay to College Station area. Not expecting much more than maybe a .10 of an inch in this region. With onshore winds in place for several days I cannot rule out a rogue showers or two at really any time over the weekend into early next week…but rainfall if any will be on the light side and highly isolated…consider yourself lucky if you see some! Skies will become partly to mostly cloudy today and this will linger through much of the coming period with some potential for dense morning fog on both Friday and Saturday mornings.

Next cold front was slated to move into the area and off the coast around Tuesday of next week, but nearly every forecast model has really backed off on the push of this front southward as the main energy heads more NE into Canada and the push of cold air and surface high pressure down the plains much weaker. Frontal boundary may limp into the region and stall which might support cooling of temperature to about 5 degrees above normal, but no big cool down looks in store for the region through next week. Rain chances have all but dried up with this front with energy displaced well to our N and NE over the Great Lakes and pesky SSW to SW mid level flow bringing the dreaded capping inversion over the area helping to limit convective growth. I suppose we could see a few showers along the stalling boundary…but widespread rainfall is not expected.

The US and TX is stuck in this pattern which is bringing warmth and dryness to much of the nation driven strongly by the large Pacific storm system off the NW US coast in the Gulf of Alaska. Extended range models keep toying with the idea of some much colder air making a southward plunge toward the middle of the month, but they continue to push the onset of the upper air buckling and changing of this zonal flow aloft back in time which brings significant doubt when and if it will happen.

Climate:

Most locations will end the month of November with less than an inch of rainfall. This follows an extremely dry October where rainfall was only about 25-35% of normal across the area. KBDI values continue to increase with the threat for wildfires rising. Brazoria County has issued a burn ban and I suspect a few more counties will be heading in that direction in December as vegetation health declines under dry conditions.

[David Reimer]

I'm surprised at the lack of activity in this thread considering what we have coming next week. If I typed all my thoughts on the matter, I would be here for two hours. In lieu of that, I'll just point out the need to watch for the possibility of severe weather in South/Southeast Texas during Monday/Monday Night. The GFS has been hinting at a secondary low pressure system developing in Deep South Texas. Combine that with the negative tilt trough moving through and high instability/moisture values and we have the ingredients for a fall severe weather event. Being so close to the coast and an onshore flow, I'm concerned about the possibility that the timing will be overnight.

We're still six days out, but that's already one concern on my list for next week. It's going to get busy in Texas!

[Srain]

I'm surprised at the lack of activity in this thread considering what we have coming next week. If I typed all my thoughts on the matter, I would be here for two hours. In lieu of that, I'll just point out the need to watch for the possibility of severe weather in South/Southeast Texas during Monday/Monday Night. The GFS has been hinting at a secondary low pressure system developing in Deep South Texas. Combine that with the negative tilt trough moving through and high instability/moisture values and we have the ingredients for a fall severe weather event. Being so close to the coast and an onshore flow, I'm concerned about the possibility that the timing will be overnight.

We're still six days out, but that's already one concern on my list for next week. It's going to get busy in Texas!

The 00Z Euro trended toward the idea of the GFS overnight. I'd like to see a bit more continuity before biting, but it does appear there may well be a rather potent Winter Storm on the horizon with potentially both Winter and Severe elements across the Southern Rockies/Southern Plains Sunday into Tuesday.

[Srain]

Morning e-mail from Jeff:

A chance for strong thunderstorms this afternoon.

Warm and muggy air mass that has been in place since late last week will be lifted by an incoming frontal boundary this afternoon. Radar currently shows showers along and east of a moisture plume off the SE TX coast extending from near Sabine Pass to offshore of High Island. This plume of deeper moisture has been very slowly working its way WNW over the last 24 hours and should spread inland along and south of US 59 today. Expect scattered showers to develop along the coast and begin to move inland over the next few hours as the dense fog burns off and surface heating starts to bubble up the low levels.

Weak cool front over NW TX will move SE today and enter our NW counties by late morning and sweep off the coast by early evening. Lift along the front will combine with an increasingly unstable air mass and increasing moisture to produce a showers and thunderstorms along and ahead of this boundary. Meso scale models are in good agreement on widespread development around noon from College Station to Lufkin which spreads SE this afternoon across most of the area. Parameters are in place for a few strong storms, but the severe threat is on the low side with weak shear. Once again this looks like a fairly decent shot at rainfall, but given the lack of rainfall with the past few events I am somewhat hesitant that widespread wetting rains will actually occur. With that said, feel that most areas will see some rainfall with the greatest amounts along and SE of US 59.

Cooling behind this front will be weak and short lived as the fast progressive pattern remains in place across the US. Instead of the record heat from the weekend highs will fall back toward the mid 70’s on Wednesday and Thursday with lows in the 50’s, both of which remain above early December averages. Weak boundary retreats northward on Thursday and this will return well above average temperatures and humidity to the region this weekend. Highs will return to the toasty 80’s by Saturday under southerly Gulf flow…but significant changes will follow.

Long Range:

After weeks warmth…some record…across much of the nation, the upper air pattern looks to finally break down from its fast progressive west to east flow to more amplification of a ridge of high pressure off the western US coast. This newly developing upper air pattern will shut off the parade of storm system into the W coast and direct the development of a downstream trough over the western US and plains. Cold air which has been bottled up in NW Canada will be unleashed into the US by this weekend and spread rapidly down the plains and into TX by early next week. Long range global models are having a hard time resolving the timing of this strong old front and how cold the post frontal air mass might be. Given past history with shallow cold air masses, will take the faster and colder solutions and expect a strong front to push into SE TX sometime early Monday and sweep off the coast during the day. Highs will be prior to the front with rapidly falling temperatures behind the boundary into the 40’s and 50’s under strong cold air advection. Some degree of energy does look to lag back in the base of the trough over the SW US post front which may keep clouds around behind the front and temper the temperature rise during the day. Still plenty of time to fine tune the affects of this pattern change and eventual air mass change…but finally some longer lasting cold air looks to be headed this way.

[Srain]

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1011 AM CST TUE DEC 04 2012

VALID 041630Z - 051200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MIDDLE TX COAST INTO

PARTS OF DEEP S TX...

...SYNOPSIS...

THE PRIMARY FEATURE OF INTEREST THIS PERIOD IS A LOW-LATITUDE

SHORTWAVE TROUGH WHICH WILL TRANSLATE SEWD FROM THE OZARK PLATEAU

AND SRN PLAINS INTO THE LOWER MS VALLEY AND NRN GULF OF MEXICO.

EMBEDDED WITHIN THIS BROADER-SCALE FEATURE...A VORTICITY MAXIMUM

OVER ERN OK AS OF MID MORNING WILL WEAKEN TODAY IN RESPONSE TO THE

SEWD PROGRESSION AND AMPLIFICATION OF A SECONDARY VORTICITY MAXIMUM

AND ASSOCIATED MIDLEVEL JET STREAK FROM WRN TX INTO THE NWRN GULF OF

MEXICO. MEANWHILE...AN ACCOMPANYING SURFACE COLD FRONT ANALYZED

FROM NEAR THE CONFLUENCE OF THE MS AND OH RIVERS SWWD INTO THE TX

HILL COUNTRY AS OF 15Z WILL CONTINUE SEWD TOWARD THE TX COAST AND

INTO THE LOWER MS VALLEY...SERVING AS THE FOCUS FOR TSTM

DEVELOPMENT.

...MIDDLE TX COAST INTO DEEP S TX THIS AFTERNOON AND EVENING...

12Z REGIONAL SOUNDINGS SHOWED THE PRESENCE OF A MOIST AIR MASS /I.E.

LOWEST 100-MB MEAN-MIXING RATIOS OF 12-14 G PER KG/ BENEATH MODESTLY

STEEP MIDLEVEL LAPSE RATES OF AROUND 7 C/KM. WHEN COMBINED WITH

LOCAL CLOUD BREAKS...THE POTENTIAL WILL EXIST FOR CORRIDORS OF

MODERATE AFTERNOON INSTABILITY WITH MLCAPE VALUES APPROACHING

1000-2000 J/KG. LOW-LEVEL UPLIFT ALONG THE COLD FRONT AND

DEVELOPING SEA-BREEZE WILL COMBINE WITH INCREASING HEIGHT FALLS/DCVA

ATTENDANT TO W TX VORTICITY MAXIMUM TO FOSTER WIDELY SCATTERED TO

SCATTERED TSTMS BY MID/LATE AFTERNOON. THE SEWD PROGRESSION OF THE

MIDLEVEL JET STREAK ATTENDING THE VORTICITY MAXIMUM WILL LEAD TO A

CORRESPONDING INCREASE IN VERTICAL SHEAR WITH THE KINEMATIC

ENVIRONMENT BECOMING SUPPORTIVE OF SUPERCELLS AND ORGANIZED LINE

SEGMENTS WITH AN ASSOCIATED RISK FOR DAMAGING WINDS AND LARGE HAIL

THROUGH THIS EVENING.

...LOWER MS VALLEY THIS AFTERNOON AND EVENING...

CONSISTENT WITH CURRENT RADAR OBSERVATIONS...LATEST MODEL GUIDANCE

SUGGESTS A GENERAL INCREASE IN TSTM COVERAGE TODAY BOTH ALONG THE

SYNOPTIC COLD FRONT AS WELL AS WITHIN THE OPEN WARM SECTOR WHERE

LOW-LEVEL CONFLUENCE IS ENHANCED. WHILE THE THERMODYNAMIC

ENVIRONMENT WILL BE COMPARABLE TO THAT ACROSS TX /I.E. MLCAPE OF

1000-2000 J PER KG/...VERTICAL SHEAR WILL BE NOTABLY WEAKER. THIS

WILL RESULT IN LESS ORGANIZED AND OUTFLOW-DOMINANT STORMS CAPABLE OF

LOCALLY STRONG WIND GUSTS AND PERHAPS SOME HAIL.

..MEAD/GARNER.. 12/04/2012

[Srain]

MESOSCALE DISCUSSION 2130

NWS STORM PREDICTION CENTER NORMAN OK

1109 AM CST TUE DEC 04 2012

AREAS AFFECTED...SERN TX...WRN-NERN LA

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 041709Z - 041845Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...SCATTERED THUNDERSTORM COVERAGE APPEARS LIKELY DURING THE

AFTERNOON FROM SERN TX INTO WRN-NERN LA. ISOLATED THREAT FOR

MARGINALLY SEVERE HAIL AND DAMAGING WIND GUSTS WILL EXIST.

HOWEVER...A WW DOES NOT APPEAR NECESSARY.

DISCUSSION...MIDDAY MESOANALYSIS SHOWS A COLD FRONT EXTENDING S-SWWD

FROM THE ARKLATEX REGION INTO SRN TX. ASCENT SPREADING EWD AHEAD OF

A SHORTWAVE TROUGH LOCATED OVER W TX IS AIDING IN THUNDERSTORM

DEVELOPMENT ALONG THE FRONT IN E-CNTRL TX. AHEAD OF THE FRONT FROM

SERN TX INTO NERN LA...PARTIAL CLEARING HAS ALLOWED TEMPERATURES TO

WARM INTO THE 70S...WHILE DEWPOINTS RESIDE IN THE UPPER 60S. GIVEN

THE PRESENCE OF MIDLEVEL LAPSE RATES FROM 6.5-7.0 C/KM...MODIFIED

12Z RAOBS YIELD MLCAPE VALUES FROM 1000-2000 J/KG. THIS

THERMODYNAMIC ENVIRONMENT COMBINED WITH A CONFLUENT SURFACE FLOW

REGIME WILL FAVOR SCATTERED STORM COVERAGE ALONG AND AHEAD OF THE

FRONT DURING THE AFTERNOON. PRIMARY LIMITING FACTOR FOR GREATER

SEVERE WEATHER POTENTIAL IS WEAK DEEP-LAYER WIND SPEEDS AND SHEAR.

HOWEVER...MODERATE INSTABILITY WITHIN THE AREA OF PARTIAL CLEARING

MAY ALLOW A FEW MULTICELL THUNDERSTORMS TO PULSE UPWARDS IN

INTENSITY AND POSE A THREAT FOR MARGINALLY SEVERE HAIL AND

STRONG/SEVERE WIND GUSTS.

..GARNER/MEAD.. 12/04/2012

ATTN...WFO...JAN...LCH...SHV...HGX...

[OKpowdah]

Wow. The GFS has become even more amplified with the s/w diving south ... which has actually not been favorable for snow in OK as the s/w cuts off then deamplifies as it gets lifted NE ahead of the next trough.

The 00z ECMWF meanwhile ... WOW wow wow. That's a legit snowstorm for the southern Plains next Monday

[ouamber]

Wow. The GFS has become even more amplified with the s/w diving south ... which has actually not been favorable for snow in OK as the s/w cuts off then deamplifies as it gets lifted NE ahead of the next trough.

The 00z ECMWF meanwhile ... WOW wow wow. That's a legit snowstorm for the southern Plains next Monday

I can't see the 12Z Euro yet, but does the 00Z lay down any snow for OK?

[Srain]

Wow. The GFS has become even more amplified with the s/w diving south ... which has actually not been favorable for snow in OK as the s/w cuts off then deamplifies as it gets lifted NE ahead of the next trough.

The 00z ECMWF meanwhile ... WOW wow wow. That's a legit snowstorm for the southern Plains next Monday

Yeah. I am becoming a bit more encouraged that we may well see a legitimate threat for New Mexico/The Panhandle on into most of the Southern Plains.

[OKpowdah]

I can't see the 12Z Euro yet, but does the 00Z lay down any snow for OK?

I don't have any snowfall maps for the Euro, but just from the PSU 4-panel charts the 00z run is most certainly a 3"+ storm for parts of OK.

[Srain]

MESOSCALE DISCUSSION 2131

NWS STORM PREDICTION CENTER NORMAN OK

0108 PM CST TUE DEC 04 2012

AREAS AFFECTED...TX COASTAL PLAIN

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 041908Z - 042115Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...A SMALL SEVERE TSTM WATCH MAY BE CONSIDERED FOR PARTS OF

THE TX COASTAL PLAIN THIS AFTERNOON-EVENING. ISOLD LARGE HAIL AND A

FEW INSTANCES OF STRONG-SEVERE WIND GUSTS ARE POSSIBLE THRU THE

EARLY EVENING.

DISCUSSION...TRENDS IN VISIBLE SATELLITE IMAGERY SHOW A SWELLING CU

FIELD INVOF A PRE-FRONTAL WINDSHIFT AND OVER A WARM SECTOR LOCATED

OVER THE TX COASTAL PLAIN. SURFACE TEMPS HAVE WARMED INTO THE LOWER

80S AMIDST AN ADEQUATELY MOIST/DESTABILIZING AIRMASS. A MID-LEVEL

SPEED MAX IS CONTINUING TO APPROACH THE REGION FROM THE CONCHO RIVER

VALLEY/EDWARDS PLATEAU REGION. UPWARD VERTICAL MOTION ASSOCIATED

WITH THE UPPER FEATURE...COMBINED WITH WEAK LOW LEVEL CONFLUENCE

ALONG THE PREFRONTAL BOUNDARY...AND DIABATIC HEATING WILL ACT TO

FURTHER WEAKEN THE CAP SAMPLED BY THE 12Z CRP RAOB. THE CAP HAS

ALREADY ERODED FROM MATAGORDA BAY NEWD TO THE SABINE RIVER...WITH

SCTD STORMS /OCCASIONAL PULSATING SEVERE UPDRAFT/ EXPECTED TO LEAD

TO SUBSTANTIAL CONVECTIVE OVERTURNING OVER THE NEXT FEW

HRS...THEREBY LESSENING THE SEVERE RISK IN THIS REGION. FARTHER

SSW...MORE SPARSE CONVECTIVE COVERAGE --LIKELY DELAYED UNTIL

MID-LATE AFTERNOON-- IS EXPECTED. UPWARDS OF 40 KT DEEP SHEAR AND A

MODERATELY UNSTABLE AIRMASS /1500 J/KG MLCAPE/ WILL SUPPORT

ORGANIZED STORM STRUCTURES CAPABLE OF ISOLD LARGE HAIL/DMGG WIND

GUSTS.

..SMITH/MEAD.. 12/04/2012

ATTN...WFO...HGX...CRP...EWX...BRO...

[DoctorMu]

Saw a little action with the Alaskan cold air earlier. Even TWC picked up on it. As sRain pointed out this will be swift and shallow. A raw day in the 40s TUE seems possible.

Maybe some mischief N of us. Would like to whack down the insects with a freeze or two.

[Srain]

Morning e-mail from Jeff:

Strong Canadian cold front will sweep across the region Sunday night ending this warm and muggy weather. Highs on Monday will struggle to reach 50 under strong cold air advection and cloud cover.

However before Sunday evening we must continue with this warm and humid air mass and the daily cycle of morning low clouds and fog followed by afternoon partly cloudy skies. Lows in the 60’s and high near 80/low 80’s may approach record values over the weekend. Moisture return off the Gulf will continue with the potential for a few scattered showers Saturday and Sunday. Amplification of the western US ridging sends a cold Canadian air mass down the plains and into TX Sunday. Will likely see a thin line of showers/thunderstorms along the front Sunday night, but once again the coverage looks meager with areas east of I-45 favored for the most activity. Maybe a few locations will squeeze out .50 of an inch.

While models have been slowing down the frontal timing, such cold air mass tend to plow southward faster than models suggest and expect the front to be off the coast by early Monday morning. The temperature will fall a good 10-15 degrees with the front and then continue a steady decline on Monday under strong cold air advection. Upper level trough remains west of the area into Monday and Monday night and this should keep clouds in place over top of the deepening frontal inversion. The combined effects of clouds and strong cold air advection will result in a cold Monday with highs in the 40’s to low 50’s with gusty NW winds of 10-25mph.

Skies might clear out early enough Monday night/Tuesday morning for near freezing conditions over parts of the area. Still expect winds to stay up some with the ridge axis just to our west, so conditions are not completely perfect for strong cooling. Better setup may come Tuesday night/Wednesday morning with ridge axis nearly overhead and mainly clear skies. Could see temperatures near or below freezing all the way to I-10 and in the rural areas away from Houston. May need a freeze warning for this time period…but much can change over the next few days especially with cloud cover.

After Tuesday, the models diverge on the prospect of the next trough affecting the area. A few models develop a coastal storm off the lower TX coast and keep the cold air locked in place with overrunning rains while other bring the warm sector inland and are much drier. I am tending to lean toward the drier solutions given the ongoing pattern this fall and the worsening drought conditions.

Fire Weather:

Some concern on Monday for fire weather conditions, but current expected cloud cover and higher RH should help mitigate strong gusty winds. Additionally, some rainfall is likely on Sunday night which should help to wet the finer fuels. Will keep an eye on this aspect over the weekend, in case RH values fall more than expected.

[Quixotic1]

chance of snow in the forecast for dfw on monday. i have doubts. i cant remember the last time it rained imby. sw flow has been the predominant one the last couple of months. any thing that falls will probably end up as virga

[DoctorMu]

chance of snow in the forecast for dfw on monday. i have doubts. i cant remember the last time it rained imby. sw flow has been the predominant one the last couple of months. any thing that falls will probably end up as virga

Good to see the cold back through after the Euro and GFS backed off yesterday.

DFW has seen its share of winter mischief the past few years, so we'll keep the fingers crossed. We even had snow in CLL on about 12/8 a few years ago.

[Ed Lizard]

Good to see the cold back through after the Euro and GFS backed off yesterday.

DFW has seen its share of winter mischief the past few years, so we'll keep the fingers crossed. We even had snow in CLL on about 12/8 a few years ago.

12/10/08 and 12/5/09, IIRC, we had miracle snows in Houston.